Homeostatic PLN structure. (A) Classification of PLN into small (Pop: popliteal), medium (Cer + Ax: cervical and axillary), and large (Ing: inguinal). Each symbol represents 1 PLN. (B) Correlation between PLN volume and number of B-cell follicles. Each square represents 1 PLN. (C) Normalized size distribution of individual B-cell follicles. ▭ indicate 1 to 5 × 10⁶ μm³; , 5 to 15 × 10⁶ μm³; , 15 to 25 × 10⁶ μm³; and ▬, greater than 25 × 10⁶ μm³. (D) Correlation between PLN volume and total HEV length. Each square represents 1 PLN.